What is the difference between O2 and O3?
Oxygen gas is necessary for living things in that it fuels the Kreb's cycle that changes carbohydrates like sugar into energy. Oxygen is reactive in that combines readily with other chemicals. However Oxygen is stable until it undergoes a chemical reaction.
Ozone is necessary for living things in that it protects living things from harmful solar radiation. Ozone being unstable reacts with and absorbs solar radiation breaking back down into normal